Low power devices, such as PDAs, cell phones, GPS units, and other similar devices, which are often, but not always, handheld electronic devices, often contain a multi-supply power supply circuit. These devices often require circuitry to provide different voltages to different functional blocks within a component, to different components, or to different circuits of the device. Furthermore, the sequence in which different supply voltages are provided to different circuits of the device or to its subcomponents or functional blocks is often critical for the operation of the device. Thus, low power devices must often sequence the voltages for its subcomponents to operate correctly.
One such method of sequencing supply voltages is shown in the device 100 shown in FIG. 1. Device 100 may be any device that requires at least a first and a second supply voltage to operate. If the device is a handheld cell phone, for example, the device may contain components such as a keyboard 102, a display 104, a memory 106, and an antenna 108. Furthermore, a bus 110 may allow different components of the device to communicate with each other or with a baseband processor 112. It should be understood, however, that the device may not include these components or may include additional components, such as a camera, a communication port, an audio port, or any other suitable component for such a device as known in the art.
The device 100 also contains a limited power source 114 labeled as VBAT. This limited power source 114 may be a battery, a charged capacitor, a solar cell, or any other suitable limited power source known to one of ordinary skill in the art. The power source is operably connected to a multi-supply power supply circuit, shown in this embodiment as a power supply chip 116, which could be a monolithic integrated semiconductor chip, that can supply different output voltages. In device 100, power supply chip 116 may supply Vout baseband processor 118 to baseband processor 112. Baseband processor may contain one or more general purpose input/output ports (“GPIOs”) such as GPIO1 120 and GPIO2 122 and up to GPIOn 124 and among other things, processes baseband information as known in the art. As one skilled in the art will appreciate, baseband processor 112 may use these GPIOs to communicate with other components. In this particular device 100, for example, GPIO1 may communicate with power supply chip 116.
Power supply chip 116 may supply and sequence several different voltages to different components of device 100, such as circuit 126, which may be processing circuitry. As shown in FIG. 1, for example, power supply chip 116 may supply and sequence supply voltages to a graphics processing unit (“GPU”) 126. As known to one of ordinary skill in the art, a GPU 126 may be operably connected to a display 104 and provide the processing capabilities to draw pictures, play movies, or perform other graphic or video functions on a display 104. The power supply chip 116 may supply Vout 1 128 to Vin 1 130 on circuit 126. Similarly, power supply chip 116 may supply a second supply voltage Vout 2 132 to Vin 2 134 and supply voltage Vout n 136 to Vin n 138. It should be understood, however, that the power supply chip 116 could supply one or more power supply voltages to any other circuit or circuits. For example, power supply chip 116 could supply one or more power supply voltages to any suitable circuitry, such as processing circuitry, a central processing unit (“CPU,” e.g., CPU core), analog processing circuitry, or any other suitable circuit known in the art.
As one of ordinary skill in the art will recognize and appreciate, a power supply chip 116 in a device 100 may perform the desired functions of, among other things, providing one or more supply voltages to the circuit 126 and sequencing them. Furthermore, however, such power supply chips do not come without disadvantages. Of particular interest, they can take up a lot of space, can be inflexible for different configurations, and can be expensive. One technique used to overcome such disadvantages is to use other power supply regulating circuits, such as low dropout regulators (“LDOs”), as shown in device 200 in FIG. 2.
FIG. 2 shows device 200, similar to device 100 of FIG. 100, which requires multiple power supply voltages. Similar to device 100, device 200 may contain a keyboard 102, a display 104, a memory 106, an antenna 108, a bus 110, a baseband processor 112, a limited power source 114, and a circuit 126, such as a GPU. Instead of containing a power supply chip 116 as the multi-supply power supply circuit, however, device 200 includes multiple power supply regulating circuits 202, 204, and 206 to form a multi-supply power supply circuit. 208. The first power supply regulating circuit 202 supplies Vout 1 210 to Vin 1 130; the second power supply regulating circuit 204 supplies Vout 2 212 to Vin 2 134; and the nth power supply regulating circuit 206 supplies Vout n 214 to Vin n 138. Device 200 may also contain additional power supply regulating circuits to provide additional power supply voltages to other components. One example of this is shown as the baseband processor power supply 216, which provides Vin 118 to the baseband processor 112.
As one skilled in the art will appreciate, these multiple power supply regulating circuits could be low dropout regulators (“LDOs”). LDOs are linear voltage regulators that can supply a Vout with a very low drop in voltage compared to Vin. LDOs may be discrete, or they may be implemented on larger integrated circuits. Multiple LDOs may even be in the same die. As shown in FIG. 2, LDOs may contain an unregulated input voltage (shown as “In” in FIG. 2), a regulated output voltage, and an enable input. As one example, an LDO may require an enable input signal of at least 1 volt to enable the LDO and may require the enable input signal to drop below 0.2 volts to disable the LDO.
LDOs in a device similar to device 200 receive their enable input signals via GPIOs from a baseband processor 112. For example, power supply regulating circuit 202 receives an enable input signal from GPIO1 120; power supply regulating circuit 204 receives an enable input signal from GPIO2 122; and power supply regulating circuit 206 receives an enable input signal via GPIOn 124. Thus, the baseband processor 112 has the ability to sequence the times at which each LDO supplies its Vout by controlling the time at which it enables each power supply regulating circuit. This is advantageous in devices that require sequencing of supply voltages.
As one skilled in the art will readily recognize, however, the implementation of a multi-supply power supply circuit shown in FIG. 2 does have disadvantages. For example, a different GPIO must enable each power supply regulating circuit, such as an LDO, to provide a required sequencing of the power supply voltages. As additional features are continuously being added to low powered, often handheld, devices, however, the number of GPIO ports can be a limiting factor to the potential expansion of such devices because a baseband processor contains a limited number of GPIOs. It is therefore desirable to efficiently use the limited number of GPIO ports on a baseband processor.
Therefore, a need exists for an improved multi-supply power supply circuit.